Dear TechNet:

I have forwarded this for your response as the question is beyond my expertise (and I know the metallurgists will have some fun....)

-----Original Message----- 
From: Nancy Capp 
Sent: Jun 11, 2007 2:35 PM 
To: [log in to unmask] 
Cc: Jeannie Bean , Pat Kelton , Randy Bethel 
Subject: PCB Solderability 


Gregg and Warren, 

We have been experiencing solderability problems with our PCB’s since we changed to lead-free solder. Our engineers have listed the IPC-4552 as the applicable specification for the ENIG finish. I believe this was suggested by the board manufacturer. 

 

Typically our processes begin with solder paste screening, SMT component placement (using pick and place machines), and solder reflow using a reflow oven. Some boards have SMT components on both sides so this process would be repeated. After cleaning and inspection, the parts go to the next phase of assembly which is hand placement and soldering of PTH components. 

 

We have been seeing some non-wetting problems after the surface mount process and reject the boards at that point without trying to do any rework of the unacceptable solder. If defects are not found, the boards go on to PTH assembly for hand placement and hand soldering of those connections. We usually then find additional defects with wetting problems related to the land and barrel of the PTH connections. These non-wetting conditions exhibit a blackish coloring which are being referred to as black pads by those in production. These defects appear to have copper showing with the gold possibly leaching into the solder. 

 

Our QA and purchasing managers have visited the facility of the board manufacturer and our engineers have had many communications with them regarding these unsolderable conditions. We have been told that the board manufacturer does not claim to be soldering experts but that they suspect that the multiple reflows or soldering processes may be having an effect on the solderability. There has also been concern expressed regarding storage of the boards as far as possible oxidation. We have been working on refining our lean processes which has reduced our inventory which in turns reduces the shelf time for our materials. Could you provide some source of information as to what our boards should be capable of? It seems unreasonable to think that the boards would become unsolderable due to the reflow processes prior to the hand soldering steps. 

 

We would greatly appreciate any information or help that you could offer us. This is a very costly problem and we are trying to work with our vendor to remedy it. Thank you for the great support that you provide. I will look forward to hearing from you. 

 

Nancy D. Capp, CIT 

Voltage Multipliers, Inc. 

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